Short answer:
At the beginning of the movement/hazard phase.
Explanation:
The hazard limit is determined for each company at the beginning of the movement/hazard phase, which is reaffirmed throughout the various ICE rulebooks. However, some players have been confused by an inconsistency in The Balrog/Challenge Decks Rules Summary, which states that the hazard limit “is set at the end of the organization phase.”
As evidence for the former, here are various citations with the relevant parts highlights:
This committee has resolved that the hazard limit is determined for each company at the beginning of the movement/hazard phase for the following reasons:The Lidless Eye Rulesbook – Player Turn Summary (page 93):
… The hazard limit is determined for each company at the beginning of the movement/hazard phase (i.e., it remains fixed).”
The Lidless Eye Rulesbook – The Hazard Limit (page 45):
Clarification: For the purposes of calculating hazard limits, each company’s size is determined for each company at the beginning of the movement/hazard phase (e.g., it remains fixed) …
The Dragons Insert – Hazard Limit Clarification:
The base hazard limit is determined (i.e., set) simultaneously at the moment a company reveals its new site or otherwise announces it is beginning its movement/hazard phase …
As the Balrog/Challenge Decks version is merely a summary of the rules, there is insufficient evidence that it should be interpreted as an update to the rules.
Several Ruling Digests are based on the rule of "at the beginning of the movement/hazard phase", such as ICE Other Queries [Q25], CoE #106 [Q4], and CoE #112 [Q3], while none refer to the end of the organization phase. To uphold the Balrog/Challenge Deck wording would invalidate these ruling digests.
The traditional way of playing the game, as per the rules, involves calculating the limit at the beginning of the movement/hazard phase. Implementing a significant change to widespread historical precedent would require a strong justification.
Consequently, a new CRF entry will be added:
Please keep in mind that this line is just an errata to an existing, specific printed rules summary.CRF – Rulings By Term – Challenge Decks
Rules Erratum: Change «is set at the end of the organization phase» to «is determined at the beginning of the movement/hazard phase»